Differentiating Between Malignant and Benign Breast Masses: Factors Limiting Sonoelastographic Strain Ratio

Abstract

Purpose: We compared strain ratio vs. qualitative elastography for the further differentiation of focal breast lesions, with special focus on limiting factors.

Materials and Methods: 215 patients with 224 histologically proven breast masses (116 malignant, 108 benign) were prospectively examined using a high-end ultrasound system (Philips iU22) with serial elastography function. B-mode scans and available mammograms were reviewed according to the BIRADS classification, raw elastogram data was analyzed qualitatively using the Tsukuba score and semiquantitatively by calculating the strain ratio (fat to lesion ratio). For diagnostic performance, Receiver Operating Characteristic (ROC) curve analysis was obtained. A sub-group analysis regarding breast density, lesion size, lesion depth and histological subtypes was performed.

Results: Mean strain ratio values were 3.04 ± 0.9 for malignant and 1.91 ± 0.75 for benign lesions (p < 0,001). The areas under the ROC curve values were 0.832 (95 % CI 0.777; 0.888) for strain ratio, 0.869 (95 % CI 0.822; 0.917) for Tsukuba score, 0.822 (95 % CI 0.768; 0.876) for B-mode ultrasound and 0.853 (95 % CI 0.799; 0.907) for mammography. Sensitivity, specificity, positive predictive value and negative predictive value of the strain ratio were 90.7 %, 58.2 %, 70.3 % and 85.1 %, when a cutoff point of 2.0 was used. Only lesion depth ≤ 4 mm was associated with diagnostic failure in the multivariate analysis of factors influencing accuracy, whereas no significant correlation between breast density and lesion size and the accuracy of the strain ratio could be found.

Conclusion: The addition of strain ratio to B-mode ultrasound increases specificity without loss of sensitivity in differentiating between malignant and benign breast tumors. Strain ratio measurements should not be carried out on tumors with a lesion depth ≤ 4 mm.

Zusammenfassung

Ziel: Ermittlung des Stellenwerts der semiquantitativen Strain Ratio (SR) in der Dignitätsbeurteilung von Mammatumoren unter Berücksichtigung limitierender Faktoren

Material und Methoden: 215 Patientinnen mit 224 Brusttumoren wurden vor Stanzbiopsie mit einem Stufe-3-Ultraschallgerät mit serieller Elastografieausstattung untersucht. Die Einschätzung des Elastizitätsscores (ES) und Ermittlung der SR erfolgten patientenunabhängig anhand gespeicherter Rohdatensätze. Die diagnostische Aussagekraft wurde durch Receiver-Operating-Characteristics(ROC)-Analyse ermittelt, eine Subgruppenanalyse hinsichtlich Brustdichte, Tumorgröße und Hautabstand erfolgte.

Ergebnisse: Die 116 malignen Tumoren wiesen eine signifikant größere mittlere SR auf als die 108 benignen Tumoren (3,04 ± 0,9 vs. 1,91 ± 0,75; p < 0,001). Die ROC-Analyse ergab für die SR einen AUC(area under the curve)-Wert von 0,832 (95 % CI 0,777; 0,888), für den ES 0,869 (95 % CI 0,822; 0,917) und für die B-Mode-Sonografie 0,822 (95 % CI 0,768; 0,876). Unter Nutzung eines Cut-off-Wertes von 2,0 weist die SR eine Sensitivität von 90,7 % und eine Spezifität von 58,2 % auf (ES 87,9 % und 73,1 %, B-Mode-Sonografie 97,4 % und 42,6 %). Die Multivarianzanalyse zum Einfluss von Brustdichte, Tumorgröße und Hautabstand zeigt eine negative Korrelation zwischen Hautabstand und Genauigkeit der SR.

Schlussfolgerung: Beide Elastografieverfahren zeigen im Vergleich zur B-Mode-Sonografie eine höhere Spezifität bei etwas geringerer Sensitivität. Bei oberflächlich gelegenen Tumoren ist die SR limitiert verwertbar.

Key words

breast - elastography - strain ratio - ultrasound - specificity

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